using System;

public class RecSum
{
    static void Main()
    {
        int value = Int16.Parse(Console.ReadLine());

        Console.WriteLine((int)rSum(value));
    }

    public static long rSum(int n)
    {
        if(n == 0)
        {
            return 0;
        }
        else
        {
            return rSum(n - 1) + n;
        }
    }
}
